Digital watermarking technology, a form of steganography, encompasses a great variety of techniques by which plural bits of digital data are hidden in some other object without leaving human-apparent evidence of alteration. Many such techniques are detailed in the cited documents.
In U.S. Pat. No. 5,841,886, the present assignee disclosed an identity card that includes digitally watermarked data, e.g., hidden in a photograph of a person depicted on the card. The '886 patent noted that a passport inspector, or the like, could compare the data resulting from decoding of the watermark with other data derived from the card (e.g., text printing, bar codes, etc.). If the data did not match, then photo-swapping or other alteration of the card could be inferred.
In accordance with one aspect of the present invention, the arrangement in the '886 patent is improved upon by providing an authentication station that includes a 2D image sensor (e.g., CCD- or CMOS-based video camera), and a computer device. The image sensor produces image data corresponding to the presented document. From this image data, the computer extracts two or more identification data. One is a digital watermark. The other can be represented in the form of a bar code, data glyphs, OCR data, etc. The processor then proceeds to check that the two identification data correspond in an expected fashion. If not, the document is flagged as suspect or fake.
In accordance with another aspect of the invention, detection of barcode, data glyphs, OCR printing, and the like is enhanced by processing plural frames of image data obtained by the image sensor.
The foregoing and other features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.